CA1207554A

CA1207554A - Method and apparatus for determining the properties of cellulose pulp

Info

Publication number: CA1207554A
Application number: CA000430265A
Authority: CA
Inventors: Kjell A. Malmgren
Original assignee: Mo och Domsjo AB
Current assignee: Mo och Domsjo AB
Priority date: 1982-06-16
Filing date: 1983-06-13
Publication date: 1986-07-15
Also published as: SE453867B; FI832142L; SE8203740L; FI832142A0; FI76642C; FI76642B

Abstract

Method and Apparatus for determining cellulose-pulp properties A B S T R A C T

A multiplicity of cellulose-pulp properties (for example kappa number) are based on measurement of the weight of the cellulose pulp. Since during the manufacturing process pulp comprises a liquid suspension, it is normally necessary to treat the extracted samples, including a drying stage, prior to weighing the sample and subjecting the same to subsequent analysis. In order not to change the pulp from a chemical and/or physical aspect, the pulp should be dried carefully, which takes a long time. As a result of the invention it is possible to exclude the time-consuming drying and weighing operations, and the invention relates to a method for determi-ning cellulose-pulp properties, in which a sample quantity of pulp is taken and analyzed chemically or physically, characte-rized by the combination of first analyzing the sample and then determining the exact amount of pulp in the analyzed sample which is necessary for calculating the pulp property in question, by causing all of the analyzed sample, or a measured part thereof, in the form of a fibre suspension of low concen-tration to pass an optical measuring means while measuring the fibre content.
The invention also relates to apparatus for determining the lignin content of cellulose pulps.

Description

The present invention re~ates to a method and apparatus for determining the properties of cellulose pulp, and mGre particularly for determining cellulo~e pulp properties where informatlon concerning the amount Gf pulp-sample analyzed is necessary in the evaluation oE the pulp-property in question. By cellulose pulp is meant here, and in the following~ both pulps which contain more-or-less no lignin, and pulps which have a high lignin content. Examples of such pulps include chemical pulp, semi-chemical pulp, thermo-mechanical pulp and mechanical pulp.

Background Art When determining, for example, the lignin content of pulps, a pulp-sample is taken and usually reacted with a 0.1 N potassium permanganate solution.
The amount of potassium permanganate in numher of millilitres of 0.1 N potassium permanganate solution consumed for each gram of bone-dry pulp constitutes a measurement of the lignin-content of the pulp. This numerical value is generally called the kappa-number.
In Scandinavia it is routine procedure to use a specified measuring method for determining the kapEa-number, known as SCAN-C 1:77.

Correct determination of the amount of samp~e analyzed is a primary general requirement of the SCAN-method. The amount of pulp concerned is determineo by weighing, and in order to know the weight of the dry pulp, the pulp being weighed must be absolutely dry, or the dry-solids content of the pulp being weighed must be known. When the sample is -taken, the dry-solids content is low, i.e. the sample contains much more water than pulp fibres. According to the SCAN-method, if the suspension is a screened-pulp suspension it is necessar~
to produce a pulp cake (3-4 grams) by filtering the pulp through a Buchner funnel. The pulp is then air-dried in a certain manner, and shredded into small pieces, ~nere-after the sample is weighed and the analysis can commence kh/~
~ .~) ~Z0~554 Aix-dryin~ of the pulp is normally effected b~ storing the pulp sample in a drying cabinet at a ternperature of 40C. Drying takes several hours, and in research laboratories it is normal for the sample to be kept in the cabinet from one day to the next, i.e. o~ernight.
When pulp is dried in this way, the dry-solids content reaches a state of equilibrium lying at about 95~.

In operational laboratories, i.e laboratories which are directly connected with the pulp-manufacturing mill, the dryin~ time is shortened by first forming a sheet from the pulp sample, and then drying the sample in a drying cabinet at 105~C to absolute dryness, before the sample is weighed. The drying times re~uîred ~ary between different pulp samples, but normally lie within the range of 45-60 minutes. The shortening o~ the dryin~
time by raising the temperature involves certain risks, irt.e_-a'ia because _he pulp sample can c~a~ge chemically as a result thereof, and consequently may not correspond exactly to the pulp being produced.

Other methods for determining the lignin content than those based on the consumption of potassium permanganate are known. One such method is described in Swedish Patent Application Number 80 00434-~, published July 18, 1981, according to which the lignin content is determined by measuring the increase in temperature which results when chlorinating a pulp sample of well defined dry-solids content. The pulp sample is de-watered by pressing the same while simultaneously blowing t~ere-through a gas which is weakly acti~e with respect to oxidation, whereafter the maximum temperature increase is recorded by blowing chlorine gas through the sample.
Although, when practicing this method, it would not seem necessary to determine the amount of sample being analyzed, particular attention must be paid to the dry-solids content.

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:12075S4 Description of the Invention Technical Problem When determining, for example, the lignin content of pulp, the step which includes determining the amount of sample taken, i.e. the drying and weighing of the sample, is extremely time-consuming, and is in fact in the order of hours. Such a long lapse from the time at which the sample was taken to the time at which the result of the analysis is established constitutes an obstacle in the correct control of the pulp-manufacturing process. It is desirable to decrease the time-lapse between taking the sample and establishing the result of the analysis, without reducing the accuracy of the analysis.
This time-consuming quantity-determining step also presents a serious problem in the determination of other pulp properties, such as the measurement of washing losses for example.

Solution The aforedescribed problems are solved by means of the present invention, which relates to a method for determining at least one property including lignin content of cellulose pulp fibers, which comprises selectins a sample of cellulose pulp to be analyzed, analyzin~ the pulp sample for the property, and determining the cellulose pulp fiber content of the pulp sample by subjecting the analyzed sample in the form of a cellulose pulp fiber suspension of low consistency to an optical measurement capable of measuring fiber content, thereby determining the property.
A prime feature of the present invention is that the quantitative measurement of the pulp is not carried out until the actual analysis of the pulp property has been made, and that the measurement is effected optically.
On the other hand, if the reverse procedure is taken, so that the quantitative measurement is made before the analysis no reproduceable result can be obtained.

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The present invention also relates to apparatus for determining at least one property including lignin content of cellulose pulp fibers, comprising means for selecting a sample o~ cellulose pulp to be analyzed, means for analyzing the pulp sample for the property, and optical measuring means capable of measuring fiber content for determining the cellulose pulp fiber content of the pulp sample, means being arranged in a sequence for first analyzing the pulp sample, and then determining the cellulose pulp fiber content by the optical measuring means, thereby determinin~ the property.
The location in the pulp-manufacturing process at which a sample is taken is partially dependent upon the pulp property of interest. ~n important property of the pulp is its lignin content. The lignin content is of '~
interest during several stages of the pulp-manu~acturing process. Normally a pulp sample is taken for determining the lignin content of the~pulp after the cooking stage and after one or more bleaching stages (for example oxygen-gas bleaching stage and chlorination stage) and after extraction stages.
The pulp concentration of the removed sample varies with the location at which the sample was taken. In order for the optical quantitative measurement to be made with great accuracy, the sample shall be present in the form of a fibre suspension having a concentration below 5%, preferably below 1%. The invention is suitable for both laboratory purposes and for operational purposes, i.e. in direct connection with the pulp-manufacturing process, and may be automatized. Treatment of :~`

~2~)7554 thc pulp sample subsequent to being taken ~rom the pulp-manu-facturing process is depcndcnt upon whether the invention is applied for laboratory purposes or is applied in direct connec-tion with the pulp manufacture. IYhen determining the lignin content of the pulp, the sample must be freed from waste liquor, and is therefore washed with water. I~hen taking a pulp sample after the digester for example, it is suitable to screen the sample. This is not necessary, however, when, for example, a sample is taken after an oxygen-gas bleaching stage. If the l~ pulp sample is taken just prior to the stream of pulp suspension entering a washing filter, the concentration is normally about ~ ~en determining the lignin content during operation, it is suitable to maintain approximately the same pulp concentration while washing and optionally screening the pulp sample, which lS means that the sample arrives at a sample-determining reaction vessel in the form of a fibre suspension having a concentration of about ~. It is fully possible, however, to increase or decrease the fibre concentration temporarily, while washing andJor screening the sample. It is also possible to remove the sample at a much hi~her concentration and to introduce the sample :;nto the reaction vessel at said higher concentration, or to thin the sample with water during its passage to said vessel. It is also possible to take the sample at a concentration of about 1% and then to increase the concentration by withdrawing liquid from said sample, and pass the sample to the reaction vessel. When applying the invention for laboratory purposes, the following procedural steps are taken for example. If the pulp sample is taken, for example, from the blow-line of the digester, the sample is screened in a so-called Wennbergs screen.
After screening the sample, the pulp is further washed in a sheet mould and formed into a sheet, which is couched with a dry blotting sheet, so as to increase the concentration to about 30~. An approximate amount is then taken from the resul-tant sample sheet, this approximate amount being about three times the calculated dry sample. In practice this is effected by the person making the analysis tearing off a certain portion of the sample, which in size is approximately the same from time to time. Since the amount of pulp is not critical, it is ` ~ ~2~7~54`

easy to establis]l ;I routinc l~itll rcsl~cct to the torn-o~f pulp-sample pieccs. The sample pieces are then dropped into the reaction vessel.
If determination of the ]ignin content is effected in accordance with the method based on the amount of 0.1 N
potassium permanganate solution consumed by the pulp in milli-litre per gram of bone-dry pulp, as in the SCAN-method for example, Appendix B, the following applies. When taking a laboratory sampl-e ln accordance with the invention, the pulp is introduced into the reaction vessel in solid form with an estimated bone-dry weight of about 1 gram. The sample is sus-pended in 400 ml of water. When sample taking is automatized in accordance with the~inven~ion, the pulp sample arrives at the reaction vessel preferably in the form of a suspension.
Thus, the reaction vessel should be able to accommodate much more than 400 ml. According to a preferred embodiment of the invention, the pulp suspension is introduced to the reaction vessel in a volumetric excess, the reaction vessel being pro-vided, for example, with a closeable spillway located at a level corresponding to a volume of 400 ml. Liquid, with or without fibres, is drained off through said spillway, until the sample volume of 400 ml is obtained. As will be understood, it is also possible to supply the pulp sample in the form of a - suspension in a volume beneath 400 ml, and then to supply water up to 400 ml or a~ove. In this latter`case, the surplus liquid, with or without fibres, must be tapped off before commencing the actual analysis. Naturally, the sample can be suspended in a volume which deviates from 4~0 ml, i.e. the volume may be both greater and smaller than 400 ml.
As will be understood from the aforegoing, when practicing the method according to the invention it is no~ necessary to keep a check on the whole of the amount of fibre which the sample comprises at the time of taking the sample. On the other hand, it is absolutely necessary to keep a check on all fibres while carrying out the analysis and subsequent to the completion of the analysis for the quantitati~e determination.

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In the SCAN-method, the sample, i.e. pulp of appro~imately 1 gram bone-dry weight suspended in 400 ml of water is admixed with 50 ml 4 N-sulphuric acid for acidification. 50 ml of 0.1 N
potassium permanganate solution is then added. The reaction is interrupted after 10 minutes by adding 20 ml of 1 N potassium iodide solution, whereafter the iodine formed is titrated with 0.~ N sodium thiosulphate solution. Starch is used as an indicator.
Thus, the chemical analysis means that the pulp suspension is furhter diluted. According to a preferred embodiment of the invention, all of the pulp suspension is charged to a collecting vessel. Despite the dilution of the sample effecte~ by adding the chemical solutions, the sample i~s preferably further diluted with a measured amount of water. This is utilized at the same time for rinsing the reaction vessel, so as to ensure that all pulp is transferred from the reaction vessel to the subsequent optical measurement of the fibre content. The collecting vessel has two functions, firstly one of collecting the pulp suspension and seco~dly one of enabling air to be evacuated from the pulp suspension when air has been mixed therein. The pulp suspension is circulated from the collecting vessel to the optical measuring means, and then back to the collecting vessel, by means of a circulation line and a pump. A collecting vessel is not always necessary, however, since the pulp suspension can be passed directly from the reaction and measuring vessel to the optical measuring means. It is also possible for one and the same vessel to function as a reaction vessel, measuring vessel and collecting or air-ventilating vessel.
The optical measuring means may be any kind of measuring means having suffisient accuracy and reliability for the purpose intended. One example Df a suitable optical measuring means is ~ fr~?Je r~
the TP21Laboratory Fibre Analyzer sold by the ComPany Eur-Control.
In this measuring device, the fibre suspension passes a trans-parent tube. Arranged on one side of the tube is a light souTce which sends a light beam through the tube and the fibre suspen-sion, via a lens. A detector is arranged on the opposite side ofthe tube, on level with the transmitted light beam. A further detector is arranged within an angle of 10 degrees from the ,: ' - I

1~Z07S54 .

firstmentioned detector. By measuring the amount of light which passes straight through the sample and the amount of light which deviates 10 degrees from said direction, information is obtained concerning the amount of fibre in the ibre suspension. For s example, it can be read-off as mg fibres per litre suspension liquid. The number of milligrams is obtained by comparing the light intensity measured at the sampling moment with previously made calibration tests. It has been found that when using said device, a particularly suitable fibre content in the pulp suspen-lG sion is 0.4-0.8 g, i.e. 400-800 mg, per litre.It is also possible, however, to measure both lower and higher fibre contents.
Since the optical measuring means gives the fibre content of the suspension in mg/l, and since exact data is found con-cerning the amount of liquid supplied from the time the pulp is introduced into the reaction vessel, it is possible, by applying simple mathematics, to calculate the amount of analyzed pulp in grams, without weighing the pulp at all.
Other types of optical concentration-measuring devices are also found on the( ma~ket )For example, one such measuring -

2 ~ device, designated ACM/ is sold by the company Cerlic Electronics AB. The measuring principle of this device is based on the ability of the cellulose fibres to absorb and reflect light. In this respect, the loss of light between transmitter and receiver provides a measurement of the fibre concentration. The light used is infra-red, transmitted in pulse form. According to information, the measuring range lies within a concentration range of 0.00005 to about 4~.
The present invention can also be used for measuring other pulp properties, such as the washing losses during pulp manufacture for example. In this analysis, pulp samples are taken and thinned or diluted with water to a given ~olume~ The il amount of washing losses, i.e. the undesirable organic and in-organic conten~ of the pulp after cooking and washing, can be deteTmined by means, for example, of ion-selective electrodes.
The pulp suspension is then passed to an optical measuring means, I
where the fibre content is determined, for example, in mg~l. i I

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~207~i54 Since the sample has been diluted with ~ater to a g;vcn ~olume, it is a simple matter to calculate the washing losses and to state said losses in, for example, kg Na2SO4 per ton of pulp.
The washing losses can also be determined by passing a small, S representative portion of the sample liquid to a flash photo-meter, and analyzing said liquid therein. In this case, the amount of sample taken must be measured and subtracted from the given volume when determining the fibre content.

Advant~
When determining the lignin content of cellulose pulp in the form of kappa numbers, in accordance with the methodology applied hitherto for example, the time taken to dry the pulp sample prior to weighing the same is of the order of hours.
When drying the sample at a temperature of 105C in accordance with the so-called quick kappa number method, the time taken to dry the pulp sample is from 45-60 minutes, to which must be added some minutes for weighing the sample. This time-consuming drying operation, and also the weighing operation, are elimina-ted when the amount of cellulose pulp sampled is determined in accordance with the invention. The optical quantitative deter-mination according to the invention, which is carried out on a sample which has already been analyzed, is completed in approxi-mately 4-5 minutes, which means that the invention enables a reliable value to be obtained with respect, for example, to the lignin content of a pulp sample at least 40 minutes quicker than has previously been possible when applying analysis techniques established within the cellulose pulp industry. This is of great significance in controlling the pulp-manufacturin~ process. Many advantages are achieved by the elimination of the necessity to weigh the pulp, this necessity at times being troublesome.
~hen the pulp sample is dried at 105C to absolute dryness in accordance with earlier techniques, ~he pulp is not in equilib-rium moisture-wise with the ambient air dùring the weighing opera~ioD, and hence the persGn weighing the sample must be extremely quick in order for a correct weighing result to be .

~07554 obtained. If part of the pulp sample is lost during passage of - the sample between the weighing station and the analyzing station it is disastrous to the result of the analysis. In the process of the invention, however, any loss of pulp fibres between the S sampling moment and ~he moment of analysis is without influence on the result of the analysis. In order to shorten the sample-treatment time, i.e. the time taken in drying and weighing the sample, it has been suggested that the pulp sample taken is divided into two parts, whereupon the dry-goods content is determined on one sample part and the analysis is made on the other sample part, which is weighed with a relatively high water content, whereafter the bone-dry weight is calculated subsequently.
In order for such a method to function correctly, however, the division of the sample into ~wo parts must be done in such a manner that both the dry content and the other properties coincide between the samples. This is extremely difficult to - achieve in practice. On the other hand, when practicing the method according to the invention it is those fibres which have already been the subject of analysis (or a given percentage thereof) which are subjected to quantitative determination.

Brief Description of the Drawings In Figure 1 there is illustrated a first apparatus array for use when practicing the invention for laboratory purposes.
Figure 2 illustrates a second apparatus array, for use when practicing the invention for laboratory purposes.
Figure 3 illustrates an apparatus array for use when applying the invention in direct connection with a pulp-manu-facturing process.
Figure 4 is a flow sheet illustrating handling of the pulp sample from the sampling location, over the chemical ana-lysis stage to the quantitative determinii~g stage in an automatized embodiment of the invention.
Figure 5 illustrates a comparison made between the lignin content of pulps (kappa number) obtained in accordance

3~ w;th the SCAN~method and in accordance with the invention.

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Prcferred Embodiment Application of the invention when determining the kappa-number of cellulose pulp will now be described with reference to Figures 1 - 4.
The array of apparatus illustrated in Figure 1 is suitable for use in laboratories, for example research laboratories and works laboratories. An estimated amount of pulp, approximately 3 g, having a concentration of about 30 ~ is introduced into the reaction vessel 1. The pulp sample has not been weighed but the laboratory assistant introduces into the vessel an amount which he judges to weigh about 3 g. 400 ml of wa~er are then added to the reaction vessel ? whereafter the pulp sample is slurried to form a suspension, by means of a propeller agitator 2.
A 0.1 N solution of potassium permanganate (KMnO4) is stored in vessel 3, while a 0.2 N solution of sodium thiosulphate (Na2S2O3) is stored in vessel 4. The pulp suspension is acidified with 50 ml of 4 N sulphuric acid ~H2SO4) measured and pipetted manuallyj whereafter 50 ml of potassium permanganate solution is supplied from vessel 3 via metering means 5, called dosimeter.
The pulp is allowed to react with the potassium permanganate supplied for 10 minutes~ whereafter the reaction is interrupted by supplying to the reaction vessel 1 20 ml of a 1 N solution of potassium iodide (KJ~. The potassium iodide solution is measured and added manually, by means of a so called vogel-pipette. Some drops of starch solution are added as an indicator. Unconsumed potassium permanganate reacts with the potassium iodide added to form iodine (J2). Occurring free iodine is titrated with the sodium thiosulphate solution in reaction vessel 1. The sodium thiosulphate solution is passed from the vessel 4 to the reaction vessel via the graduated metering means 6. The amount of sodium thiosulphate solution added is noted at the end point, whereafter an equivalent amount of iodine and potassium permanganate are calculated. Since information is available with respect to the amount of potassium permanganate added and the amount of un-consumed potassium permanganate, there is obtained bv subtraction the amount of potassium permanganate which has reacted with the pulp .

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The contcnts of ~he reaction vessel 1 are poured into the measuring vessel 7. The reaction vessel is thorougly rinsed with water, so that all fibres subject to analysis are trans-ferred to the measuring vessel 7. This is graduated, and the water is supplied to the pulp suspension thro~gh line 8, up to a mark showing 2 litres. The resultant suspension is then trans-ferred, via line 9, to the collecting and air-purging vessel 1~.
A stream of suspension is taken from the vessel 10 and moved in a closed circuit by means of pump 11 and circulation line 12.
As the suspension circulates, it passes an optical measuring means 13, which incorporates, inter alia, a transparent bulb, a light source, detectors and a unit for registering and calcu-lating measurement signals. The capacity of the pulp 11 is such as to constantly maintain the fibres in the suspension in motion and uniformly distributed therein. Since the sample comprises approximately 1 g of bone-dry pulp and the pulp is suspended in ~ litres of water, the pulp concentration is approximately 500 mg/l. Subse~uent to the pulp suspension having passed the optical measuring means 13 a repeated number of times, there is obtained a signal which, with the aid of previously made callibra-tion tests, provides information of the exact fibre content in mg/l. Since the volume is known ~2 litres) the amount of pulp in grams is readily obtained. The kappa-number of the pulp is obtained by dividing the amount of potassium-permanganate solution consumed in millilitres with the amount of pulp expressed in grams. I~hen measurement of the fibre content of the pulp suspension is completed, th~ suspension is passed to a drain, through the line 14.
Figure 2 illustrates a simplified array of apparatus for laboratory purposes, in which the Teaction vessel and the measuring vessel are one and the same vessel. Sodium thiosulphate solution is stored in the vessel 15 and passed to the measuring and reaction vessel 17 through the metering means 16. The potassium permanganate solution is stored in vessel 18 and is passed to the reaction and measuring vessel 17 through the metering means 19. The pulp sample, which has an approximate bone-dry weight of . .

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~o~554 1 g, is charged to the vessel 17, whereafter 400 ml of ~.ater are supplied to the vessel through the line 20. The pulp sample is slurried by means of the propeller agitator 21 to form a suspension, whereafter the chemical analysis is carried out in the aforedescribed manner. Upon completion of the analysis, further water is added through the line 20, so that the level o liquid rises to the mark denoting 2 litres. The suspension is then tapped-off through line 22 and passed to the collectlng and air-purging vessel 23. The suspension is passed from this vessel into a closed circuit for a repeated number of times, through the line 24 and the vessel 23 by means of ~he pump 25.
During its passage around the closed circuit, the suspension passes the optical measuring means 26, for measuring the fibre content in mg/l. Subsequent to terminating the quantitative determination, the suspension is passed to a drain, via the line 27.
Figure 3 illustrates an apparatus array which is more automatiz.ed than the arrays of apparatus illustrated ln Figures 1 and 2. The Figure 3 embodiment of the invention is primarily intended for use in the mill, for example in the digester house and/or the bleaching department.
In the centre of the array there is located a combined measuring and reaction vessel 28~ The pulp sample is supplied to the vessel 28 in the form of a suspension of low concentration, through the line 29. The amount of suspension charged is not critical, and may reach, for example, to 700-800 ml. Subsequent to supplying : this amount of the suspension to the reaction vessel 28, a valve on the line 30 is opened~ so as to drain the suspension down to a level with the outlet of said line. This will leave 400 ml of suspension in the vessel 2~. If desired, the suspension can be agitated by means of the propeller agi-tator 31. The sodium thiosulphate solution is stored in the vessel 32, and is supplied to the reaction vessel through the metering means 33. The potassium permanganate solution is s~ored in the vessel 34 and is supplied to the reaction vessel via the metering means 35. The sulphuric acid solution is stored in the vessel 36 and is supplied to the rection vessel via the metering means 37O The potassium iodide solution is stored ~ ' ~207~iS4 - -in the vessel 38 and is p~lssed to thc leaction ~csscl via thc metering means 39. Subsequent to adding sulphuric acid and potassium permanganate to the suspension, the lignin-containing pulp is permitted to react with the potassium permanganate for a given length of time. According to the SCAN-method a reaction time of 10 minutes shall be employed. The reaction time, however, can be reduced to, for example, 5 minutes. The reaction is interrupted by introducing potassium iodide. Sodium thiosulphate is then added, for reaction with the iodine formed. Inserted into the reaction vessel 28 is a pair of redox electrodes, platinum-electrode 40 and reference-electrode 410 The redox-electrode pair extend from the end point titrator 42, which is connected to the means 33 for metering the sodium thiosulphate solution. I~hen all iodine has been consumed by reaction with lS sodium thiosulphate, a- jumping change in the redox potential takes place, whereupon the supply of sodium thiosulphate solution is terminated and the amount added can be read-off from the metering means 33. Subsequent to finalizing the chemical analysis, it remains to determine the amount of pulp sample used.
In order to bring the pulp suspension to a concentration suitable for the optical measuring operation, the suspension is further diluted by adding water through the line 43. The water is supplied so that the level of liquid rises to, for example, the two litre mark on the graduated reaction vessel 28. The suspen-sion is passed to the collecting and air-purging vessel 45 through the line 44. The suspension is caused to circulate through the line 47 and the collecting vessel 45 in a closed circuit~ by means of pump 46. During its passage around the circuit, the flow of suspension repeatedly passes the optical measuring means 48. With respect to the thinning or dilution of the suspension in the reaction vessel 28 with water, it is not necessary to thin the suspension to th~ intended volume in one stage~ preferably the suspension is thinned in a first stage to a given volume and then passed to the collecting vessel 45.
A further measured amount of water is then supplied through the line 43, this fur~her quantity of water functioning at the same time as a rinsing liquid, for the purpose of removing all pulp fibres from the reaction vessel Z8. I~Then the quantitative determination has been made, the pulp suspension is passed to a drain through the line 49.

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In the apparatus array in which tlle method according to the invention is carried out, it is not necessary to take any manual measures, since determination of the lignin content of the pulp takes place purely automatically. It is possible, 5 however, to take some manual steps even with this embodiment of the invention. For example, the situation can arise in practice that someperson in the digester house or bleaching department may wish to determine the kappa number of pulp taken from a continuous web and at a location where the pulp is not present in the form of a suspension. In such a case, the pulp sample is released in solid form and passed by hand down into the reaction vessel 28, whereupon water is supplied through the line 43 up to a level with the outlet for line 30, i.e.
to a volume of 400 ml. In this case it is necessary to use the propeller agitator 31, to release the pulp fibres in the water to form a suspension suitable for chemical analysis.
Figure 4 is a flow sheet illustrating a fully automatized embodiment of the invention. The Figure illustrates the path moved by the pu~lp sample from the extraction location directly in a pulp-transport line via washing and optional screening, chemical analysis, optical quantitative determination, to its discharge through the drain. The Figure also illustrates collec-tion of data and the use of computer for calculating the kappa number.
The line 50 is arranged to convey, for example, unbleached pulp in the form of a suspension. Connected to the line 50 is a sample taXing device 51. A number of sampling devices are found on the market, and any one of these can be chosen. The sample volume is dependent upon the pulp concentration in line 50. The volume is adapted so that the bone-dry weight of the pulp intro-duced into the reaction vessel 52 is about 1 g. The sample taken is passed through the line 53 to a vessel 54, in which the pulp is washed and optionally screened. Clean water is passed to the vessel through the line 55, and water containing washed-out and optionally screened impurities leaves the vessel through the line 56. The sample volume can be readily corrected in this stage if so desired. The washing and optional screening in , ~207S5~ -~ssel 54 nlust be carlied out accurately, so tl~t no washin~
losses (organic and inorganic compounds) accompany the pulp sample into the reaction vessel 52. The washed and optionally screened sample is passed to the reaction vessel 52 through the line 57. Sulphuric acid is passed from the storage and metering vessel 58 to the reaction vessel 52, through the line 59. Corresponding means for potassium iodide are referenced 60 and 61, while corresponding means for potassium permanganate are referenced 62 and 63 and for sodium thiosulphate 64 and 65.
An end point titrator 66 provided with a pair of electrodes is arranged in the reaction vessel 52 in order to detect when all iodine has been consumed by the sodium thiosulphate supplied.
The function of the end point titrator can also be incorporated in a computer. Upon conclusion of the chemical analysis J water is passed through the line 67 to the volumetrically graduated reaction vessel 52. The pulp suspension is then passed through the line 68 to the optical quantitative determining means 69.
Subsequent to determining the fibre content, for example in mg/l, the pulp suspension is passed to the drain means, through the line-70.
The whole handling of the pulp sample from the extraction location to its discharge to the drain means, and all peripheral equipment for establishing the lignin content of the sample taken expressed in kappa number, are controlled ~otally from a control unit 71, which includes a computer. The broken lines illustrate that the various devices are connected to the control unit 71. All steps from the step at which a signal is trans-mitted to the effect that a sample of the pulp shall be taken to the step where a signal is sent to the effect that the sample upon which an analysis has been concluded shall be sent to the drain means are controlled by means o the computer. When applying the invention in analyzing the lignin content of the pulp it is not possible to follow the same continuously, but that the lignin content mus* be determined intermittently. In comparison with previously known analysis ~echniques based on the supply of chemicals in aqueous solutions and titrimetry, ~hen practicing the present invention, however, the total time taken from the time at which the sample is extracted to the time at which infor~ation is obtained concerning the kappa number is considerably reduced.
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.,`, , ' ~207~iS4 The time t~kcn in this rcspect i5 about 20 minutes. A
considerable part of this time, namely 10 minutes, is consumed by the time which lapses from the moment at wllicll the potassium permanganate is added to the time at which the reaction between the pulp and the potassium permanganate is interrupted, by adding potassium iodide. According to SCAN-standards this length of time shall pass, although it is fully possible to reduce this time to, for example, 5 minutes, which means that the total circulation time is lowered to about 15 minutes. This considerably improves the possibilities of controlling different steps in the pulp-manufacturing process, since the affect of different measures on the lignin content of the pulp will be brought to the knowledge o~ the operator, if not instantaneously within a comparatively short time and with a high degree of accuracy.
In order to further illustrate the method according to the invention, there is given below a number of working examples relating to laboratory tests carried out in accordance with known techniques and in accordance with the present invention.

Example 1 Two pine pulp samples and two birch pulp samples were taken from four locations in a sulphate pulp mill. The pine pulp was taken in part directly after the digester and in part after subjecting the pulp to an oxygen-gas bleaching process. The birch pulp was taken in part after the screening department and before the first bleaching stage, and in part after the first extraction stage.
The kappa number of the pulp samples were determined in ~
part in accordance with known techniques and in part while practicing the invention.
By known techniques is meant here a modified SCAN-method (SCAN-C 1:77, Appendix B). The extrac~ed pulp samples were treated in the following manner. The pine pulp taken directly after the digester was screened in a so-called l~ennbergs screen. After screening the pulp, the pulp was further washed in a sheet mould and shaped to sheet form, which was couched with a dry blotting sheet, so as to increase the concentration of the pulp - -1:~075~;~

to about 30 ~0. The sheets were then dried in a drying cabinet to 105C, until they were absolutely dry. The time taken to dry the sheets was 45-60 minutes. When the sheets had reached abso-lute dryness, a suitable sample quantity, i.e. about 1 g, was quickly weighed on analysis scales, to an accuracy of 0.001 g.
The pulp samples were then transferred to a titration vessel, where the chemical analysis was carried out in accordance with SCAN-standards. The remaining pulp samples were treated in a similar manner, with the exception that screening was excluded.
The chemical analysis provided data of the amount of 0.1 potassium permanganate solution consumed in millilitre by the different samples. By dividing these numerical values with respective weights of the weighed samples, information was obtained concerning the kappa number of the different samples.
15The following steps were taken when proceeding in accordance with the present invention. The extracted samples were washed and formed into sheets in the aforedescribed manner.
- In the case of-.the pine pulp samples taken directly after the digester, these were also subjected to screening, similar to the aforedescribed. From the wet sample sheets thus obtained was taken an estimated amount, about 3 times dry sample. The sample pieces were obtained by manually tearing the wet sample sheets. Quite simply, the laboratory assistant tore from the sample sheets pieces of approximately the same mutual size.
Since the amount of pulp was not critical, it was easy to establish a routine with regard to ~he size of the sample pieces.
The apparatus array illustrated in Figure 1 was used when carrying out the tests accoIding to the invention. The aforementioned sample pieces were placed in the reaction vessel 1 and the chemical analysis carried out completely in accordance with SCAN-standards. With regard to the chemical analysis, full conformity existed between the two test series. This means that the ~pparatus identified in Figure 1 by references 1, 2, 3, 4, 5 and 6 were used in both series. In ~he test series according to the inven~ion, the pulp samples were transferred from the reaction vessel 1 to the measuring vessel 7. The pulp ~.2o7S54 .
samples comprised a suspension containing about 1 g pulp fibres, 400 ml initially supplied water, 50 ml sulphuric-acid solution, 50 ml potassium-permanganate solution, 20 ml potassium-iodide solution, some drops of starch solution, and a given number of ml sodium-thiosulphate solution varying with the lignin content of the pulp sample supplied. Water was introduced into the graduated measuring vessel 7, through line 8, up to the mark indicating a volume of 2 litres. This means that the fibre content of the suspension lay at around 500 mg/l. The fibre suspension was tapped-off into the collecting and air-purging vessel 10. The.fibre suspension was caused to circulate, by means of a pump 11, from the vessel 10, through the pump and through line 12, back to the vessel 10. While circulating, the fibre suspension passed through an optical measuring means sold by the company Eur-Control under the name TP2 Laboratory Fibre Analy~er. The operational mode of this measuring means has been earlier described. The measuring signals obtained were compared with measuring~signals obtained in previous calibrat;ng tests, thereby providing information concerning the fibre content in mg/l. Information concerning the amount of analyzed sample in grams was also obtained hereby. The kappa number of the pulp samples was obtained by dividing the consumption of potassium permanganate in millilitre with the amount of sample in gram.
The result achieved is shown in Figure S, where the measuring results obtained is plotted in a dispersion diagram with kappa number measured totally in accordance with the SCAN-method on one axis and the kappa number measured while applying the method according to the invention on the other axis.
As previously mentioned, four different pulps were analyzed in accordance with the two methods. The following symbols were used.
= Pine pulp after digester ~= Pine pulp after oxygen-gas bleaching 3~ X = Birch pulp before first bleaching stage E3= Birch pulp after first extraction stage .. .

.

~207S54 Thc follo~ling procedure has been followed ~hen plot~ing the measuring rcsults; if, for example, a given extracted pulp sample had given a kappa number of 30 according to the SCAN-method and 32 when applying the method according to the invention, an imaginary line was drawn from the numerical value 30 on the y-axis parallel with the x-axis and a further imaginary line was drawn from the numerical ~alue 32 on the x-axis parallel with the y-~ axis, and a dot was placéd where these imaginary lines inter-sected one another. This means that if exactly the same numerical values are obtained in both analyses methods, al~ points will fall on a line which extends from the point of intersection `-bétween the two axes and which has à slope of precisely 45C.
63 comparison tests were plotted on the diagram. It was found by linear regression analysis ~carried out in the manner described on pages 323 and 324 of the book "Statistical Package for the Social Sciences", second edition published by McGraw-Hill Book Company) of the measured pair values that the following relation-ship preuails. be.tween the measured numerical values !
Kappa numberscAN = 1-07- Kappa numberInventiOn . .

Dispersion of the separate dots around this line is . very small, evident from the fact that the correlation coefficient r (calculated in the manner described on pages 280 and 281 of the book '7Statistical Package for the Social Sciences", second edition published by McGraw-Hill Book Company) is 0.999. The ideal value of r is.l.0, from which it can be seen that the correlation achieved is surprisingly good.
. It will be seen ~rom the above formula that the kappa number measured while applylng the invention is somewhat lower than the kappa number measured totally in accordance with the SCAN-methodO The reason.for this difference has not been estab-lished, although it may be due.- to the different treatment processes to which the pulp samples were subjected. In the analysis made in accordance with the SCAN-method, the samples were dried at high temperatures = 105C prior to the chemical " . I

~207~54 analysis, while when carrying out the method according to the invention the samples were not dried, and the pulp was intro-duced into the reaction vessel at a pulp concentration of about 30 %. Similar differences have been observed when making compari-sons between kappa numbers of pulps which had been dried attemperatures of 105C and at temperatures of 40C, both drying procedures being in accordance with the SCAN-method. It would appear from earlier tests made by us that relatively quick drying of the pulp at high temperatures leads to a higher kappa number compared to the case when the pulp is not dried at all or is ,dried very leniently.
The aforeillustrated good correlation between kappa number measured totally in accordance with the SCAN-method and kappa number measured while applying the invention illustrates that it is possible to decrease the total treatment time when determining the kappa number of pulps, by at least 40 minutes while maintaining a high degree of accuracy in the analysis.

Exempel 2 Sulphate pulp was taken directly after the digester.
The pulp was analyzed in part in accordance with the SCAN-method tdrying the pulp for 45-60 minutes at a temperature of 105C~
and in part while applying the method according to the invention, implying that the pulp was neither dried nor weighed prior to the chemical analysis. The pulp sample taken was screened and washed in the same manner as that described at the beginning of Example ]. Ten analyses were made in accordance with respective methods. The measuring results obtained are set forth in Table 1.

,-~207S54 Table 1 Kappa number accordingKappa number according to the invention to the SCAN-method 31.5 32.9 31.3 33.2 31.6 33.5 31.4 33.4 31.0 33-5 31.4 33.5 30.8 - 33 7 31.6 33.6 31.2 33.5 31.3 33.3 Mean value 31.3 33.4 Disperson 0.26 0.23 The dispersion = S is calculated in the adopted manner, described, for example, on page 184 of the book "Statistical Package for the Social Sciences", second edition published by McGraw-Hill Book Company.
As will be seen from the mean value of kappa numbers measured in accordance with respective methods, a somewhat lower numerical value was also obtained in these tests when carrying out the method according to the invention. It will also be seen that the dispersion in the measuring results obtained is surprisingly small in both methods.
This shows-that when applying the method according to the invention it is possible to obtain accurate information concerning the lignin content of the pulp in a much shorter time than was previously normal, calculated from the time at which the pulp sample was extracted to the time at which the kappa number is calculated, which greatly facilitates the control of ~he different pulp-manufacturing stages.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for determining at least one property including lignin content of cellulose pulp fibers, which comprises;
(1) selecting a sample of cellulose pulp to be analyzed;
(2) analyzing the pulp sample for said property; and (3) determining the cellulose pulp fiber content of the pulp sample by subjecting the analyzed sample in the form of a cellulose pulp fiber suspension of low consistency to an optical measurement capable of measuring fiber content;
thereby determining the said property.

2. A process according to claim 1 which comprises, after analyzing the pulp sample but before determining the cellulose pulp fiber content, diluting the pulp sample with a measured quantity of water to a consistency below 5%.

3. A process according to claim 1, which comprises, after analyzing the pulp sample, passing the sample to a collecting vessel, withdrawing the pulp sample therefrom and subjecting said sample to the optical measurement, and then returning said sample to the collecting vessel.

4. A process according to claim 1, which comprises, in the determination of the cellulose pulp fiber content of the sample, comparing signals from the optical measurement with calibrated signals thereof.

5. A process according to claim 1 which comprises washing the pulp sample prior to the analysis.

6. A process according to claim 1 which comprises molding pulp sample into a pulp sheet prior to the analysis.

7 . Apparatus for determining at least one property including lignin content of cellulose pulp fibers, comprising (1) means for selecting a sample of cellulose pulp to be analyzed, (2) means for analyzing the pulp sample for said property, and (3) optical measuring means capable of measuring fiber content for determining the cellulose pulp fiber content of the pulp sample;
said means being arranged in a sequence for first analyzing the pulp sample, and then determining the cellulose pulp fiber content by the optical measuring means, thereby determining the said property.

8. Apparatus according to claim 7 in which the means for analyzing the pulp sample comprises means for titration of the sample;
and the optical measuring means comprises a measuring vessel for pulp sample; means for circulating the pulp sample passed the optical measuring means while maintaining a uniform distribution of pulp fibers in the sample, a light source; detectors for detecting light passing through the pulp sample; and means for registering and calculating signals emitted by the detectors.

9. Apparatus according to claim 8 in which the means for titration of the sample comprises an end point titrator having an electrode pair arranged in a reaction vessel for sensing a change in redox potential of the sample.

10. Apparatus according to claim 7 comprising a collecting vessel arranged between the means for analyzing the pulp sample and the optical measuring means.

11. Apparatus according to claim 7 arranged for automatically determining the cellulose pulp property, comprising means for withdrawing a sample of cellulose pulp to be analyzed from a cellulose pulp stream in fluid flow connection with the means for analyzing the pulp sample; a fluid flow connection between the means for analyzing the pulp sample and the optical measuring means; and means in fluid flow connection with the optical measuring means for withdrawing the pulp samples from the apparatus following the determination; and means for sensing and collecting measurement parameters and final calculation of the cellulose pulp property.